1. Field of the Invention
The present invention relates to a photographic printer, and more particularly, to a photographic printer which uses a color light intensity control panel having a plurality of cells disposed in a matrix and can adjust the color balance and intensity of a printing light with high precision.
2. Description of the Prior Art
With a conventional photographic printer, characteristic values such as large area transmittance densities (LATD) of red, green, and blue colors are first obtained through photometry of a photographic film such as a negative film, and then the exposure amount for each color is calculated using the characteristic values. In accordance with the calculated exposure amount of each color, the positions of cyan, magenta, and yellow color filters within the printing optical path are changed to adjust the color balance and intensity of a printing light and print a color image of good quality on a color paper.
A photographic printer using three primary color filters, however, requires a filter driver for inserting each color filter into the printing optical path, and a mixing box for uniformly and sufficiently diffusing the printing light transmitted from the three color filters, the mixing box being constructed of a rectangular tube having an inner mirror surface and diffusing plates at opposite ends thereof. These components become an obstacle against realizing a compact and low-cost photographic printer. Furthermore, color filters are required to be advanced and retracted, resulting in a complicated structure of the printer and a possible failure in durability and reliability. Still further, it is difficult to control the mixing characteristics of a mixing box.
The gradation of a negative film or a color paper is uniquely determined from the characteristics of the same photosensitive material. Therefore, a problem arised in that it is difficult for a photoprint to be finished either in a soft gradation or a high gradation as desired. Furthermore, both the bright and dark portions of a high-contrast subject cannot be reproduced, but one of the portions results in poor gradation, because of the specific characteristics of photosensitive material. Still further, a frame of extremely under-exposure or over-exposure loses its gradation balance, making a proper color reproduction impossible.
A photographic printer uses various optical elements such as lamps, filters, a printing lens, a black shutter, and the like. If the characteristic of an optical element changes at each local position thereof, density unevenness (irregularity) and color unevenness (irregularity) will be produced on a photoprint. Density and color unevenness caused by the insertion of color filters can be eliminated by a mixing box. Density and color unevenness caused by a peripheral light amount ratio of a printing lens is corrected by using an optical element having a characteristic opposite to such an unevenness pattern, such as a parabolic filter or color filter.
However, unevenness of a light emission intensity of a lamp (light source unevenness) changes from one lamp to another. In practical designs and manufactures, it is difficult to manage the unevenness characteristic of each lamp so as to make it substantially constant. Although such unevenness can be dissolved by using a mixing box having a high diffusion degree, the light amount of a printing light lowers greatly, resulting in a low printing speed. In the case of a printing lens, an unevenness pattern of a printing lens changes with a magnification factor of the lens. Therefore, it is necessary for a photographic printer having a variable printing magnification factor to prepare a plurality of filters according to the number of magnification factors, which is not suitable for practical use. A black shutter also produces exposure unevenness which changes with an exposure time.